A ball sails through the air with an initial velocity of 4m/s. It bounces off of a wall over 0.5 seconds and then has a velocity of -2m/s (in the opposite direction). What was the acceleration of the ball when it bounced off the wall? m/s²

The period of a pendulum varies directly as the square root of the length of the pendulum and inversely as the square root of the acceleration due to gravity. find the period when the length is 144 cm and the acceleration due to gravity is 980 cm per second squared, if the period is 7pi seconds when the length is 289 cm and the acceleration due to gravity is 980 cm per second squared.